Investigating the optimum lower energy threshold of a new research PET/CT scanner

An investigation of the optimum 3D lower energy threshold (LET) setting of the Discovery-RX, a new LYSO based GE research PET/CT scanner is conducted. Sensitivity and noise equivalent count rate (NECR) performance of the scanner in 3D mode were evaluated at multiple LET settings: 400, 425, 450, 460, 470 and 480 KeV. The performance evaluations were conducted according to the NEMA NU2-2001 standard. In addition, the NECR was also evaluated for the same LET settings using the Data Spectrum whole body phantom in order to more accurately simulate a true clinical setting. For the sensitivity measurements, the line source was filled with 9.25 MBq of F-18. For the NECR measurements, the NEMA and the Data Spectrum phantoms were fitted with a line source having an initial activity of 1400 MBq of F-18. As expected, the sensitivity decreases with increasing LET. The sensitivity at 400 and 450 keV was 13.2% higher and 18.9% lower than the sensitivity at the scanners default LET of 425 keV. Also as expected, the scatter fraction (SF) decreased with increasing LET for both NECR phantoms. The NECR curve corresponding to the 450 keV had the highest values over the clinical range of activity concentration usually used. Initial performance evaluation suggests that a LET of 450 keV is the best setting for the phantoms tested. Further clinical tests are needed to validate this observation